The main noise sources of Perkins diesel generator set are generated by diesel engine, including exhaust noise, mechanical noise and combustion noise, cooling fan and exhaust noise, air inlet noise, generator noise, noise generated by transmission of foundation vibration, etc.
1.Exhaust noise.
Exhaust noise is a kind of high-temperature and high-speed pulsating air flow noise, which is one of the most energetic engine noise. Its noise can reach more than 100 dB, and it is the main part of the total engine noise. When the Perkins generator works, the exhaust noise is directly discharged through the simple exhaust pipe (the original exhaust pipe of the generator set), and with the increase of air flow speed, the noise frequency is also significantly increased, which has a serious impact on the life and work of the neighboring residents.
2.Mechanical noise and combustion noise.
Mechanical noise is mainly produced by the vibration or mutual impact caused by the periodic changes of gas pressure and motion inertia force during the operation of each moving part of the engine. It has the characteristics of far noise propagation and low attenuation. Combustion noise is the structure vibration and noise produced by diesel during combustion.
3.Cooling fan and exhaust noise.
Fan noise is composed of eddy current noise, rotating noise and mechanical noise. Exhaust noise, airflow noise, fan noise and mechanical noise will be transmitted through the exhaust channel, thus causing noise pollution to the environment.
4.Air inlet noise.
The function of the air inlet channel is to ensure the normal operation of the engine and create good heat dissipation conditions for the unit itself. The air inlet channel of the unit must be able to make the air inlet smoothly enter the machine room, but at the same time, the mechanical noise and air flow noise of the unit will also radiate to the outside of the machine room through this air inlet channel.
5.Transmission noise of foundation vibration.
The strong mechanical vibration of diesel engine can be transmitted to all parts of the outdoor through the foundation, and then radiate noise through the ground.
The principle of noise reduction treatment for diesel generator room is to use sound-absorbing materials and noise reduction and silencing devices to reduce the noise of air intake and exhaust channels and exhaust system on the premise of ensuring the ventilation conditions of diesel generator set, i.e. without reducing the output power, so as to make the noise emission reach the national standard (85dB).
The fundamental method of noise reduction of generator is to start from the sound source and adopt some conventional noise reduction technologies, such as muffler, sound insulation, sound absorption, vibration isolation and so on.
1.Reduce exhaust noise.
Exhaust noise is the main noise source of the unit, which is characterized by high noise level, fast exhaust speed and difficult to control. The noise can be reduced by 40-60 dB (a) by using a special impedance type compound muffler.
2.Reduce the noise of axial flow fan.
Two problems must be considered when reducing the noise of the cooling fan of the generator set. One is the allowable pressure loss of the exhaust passage. The second is the required noise reduction. In view of the above two points, the resistive chip muffler can be selected.
3.Sound insulation, absorption treatment and vibration isolation of machine room:
(1). Sound insulation of machine room. After the exhaust noise and cooling fan noise of the unit are reduced, the remaining main noise sources are the mechanical noise and combustion noise of the diesel engine. The method adopted is to remove all windows except the necessary interior wall observation windows connected with the observation room, all holes and holes shall be tightly sealed, and the sound insulation of brick wall shall be more than 40 dB (a). The doors and windows of the machine room shall be fire-proof and sound proof.
(2)Air inlet and exhaust. After the sound insulation treatment of the machine room, the problem of ventilation and heat dissipation in the machine room shall be solved. The air inlet shall be set in the same straight line with the generator set and the air outlet. The air inlet shall be equipped with a resistive chip muffler. Since the pressure loss of the air inlet is also within the allowable range, the air volume in and out of the machine room can be naturally balanced, and the ventilation and heat dissipation effect is obvious.
(3)Sound absorption treatment. Besides the ground, five walls in the machine room can be used for sound absorption. According to the spectrum characteristics of the generator set, the perforated plate resonance sound absorption structure is adopted.
(4)The exchange of indoor air and the sound insulation of the machine room will prevent the air in the machine room from convection when the closed water-cooled generator set is shut down, and the high temperature in the room will not be reduced in time. The problem can be solved by using low-noise axial-flow fan with resistance chip muffler.
(5)Genset vibration isolation. Before the installation of the generator set, the vibration isolation treatment shall be carried out in strict accordance with the relevant data provided by the manufacturer to avoid the long-distance transmission of structural sound, and the air sound shall be radiated continuously during the transmission, so that the noise level at the boundary of the plant cannot reach the standard. For the existing generator units that need to be treated due to exceeding the standard, the vibration of the ground near the unit must be measured. If the vibration sense is obvious, the generator set must be isolated first.
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